There have already been described timepieces in which the movement is mounted in a case comprising two shells, at least one of which is of transparent material, such shells being applied against one another. In particular, the timepiece described in patent CH 110 141 is of this type. In this patent however, the shells are assembled by means of an extensible metallic circle placed on the joint between the shells and gripping the latter in such a manner that such joint is no longer apparent once the circle is put into place Such circle accentuates the outer contour of the watch and takes away therefrom the lightness of appearance which it could have if such circle were absent or at least invisible.
A solution permitting to confer to a wristwatch case the appearance of being substantially thinner than its real thickness, in particular to the wearer, while offering more wear resistance and rendering it less vulnerable vis-a-vis outer stresses, has already been set out in patent EP-B-0 168 010 (U.S. Pat. No. 4,637,734). This solution consists in employing a crystal having the form of a substantially spherical cap, at least a part of the periphery of which is located at a level below that of the dial. In this patent, however, the back cover of the watch is flat, secured as it is onto a caseband which is visible and which includes bracelet attaching means, these also visible.
The purpose of this invention is to give to the case the appearance of being thin, this impression being however still more emphasized than in the watch described in the patent EP-B-0 168 010. On the other hand, the applied one against the other, gives to the watch case a new and original design aspect.